1. Field of the Invention
The present invention relates generally to molding machinery and methods, and in particular relates to a construction for blow pins for molding machines that utilizes a separable construction employing a replaceable cutting ring.
2. Description of the Prior Art
The term "blow molding" refers to a process widely used to produce bottles from high density resins, such as polyethylene. In the blow molding process, the resin is melted and formed in a viscous, semi-fluid mass. This mass is forced about a mandrel and through an extrusion orifice which shapes the resin into an elongated, thin-walled tube called a "parison." The parison is then positioned around a blow tube and within an opened, two-part mold. After closing of the mold, a blast of air is expelled through that portion of the system known as the "blow pin" to expand the parison to the interior mold wall to form the bottle. The formed bottle is then cooled on the mold walls, and the blow pin is then automatically pulled upwardly. A portion of the blow pin includes a cutting surface which then shears the bottle neck and forms a round hole in the top of the bottle.
Conventional blow pins typically comprise a single, machined unit having an upper portion with an inwardly beveled radius to receive the plastic pushed inwardly by the two mold halves, and terminating at a cutting edge, or shear surface. This single machined blow pin further includes a bottom portion that extends downwardly and receives an internal sleeve having air holes therein, the holes communicating with holes in the blow tube to permit air to be driven outwardly through the blow pin into the parison as described above.
Blow pins of the type described above are relatively expensive machined parts, but must be replaced each time the shear surface becomes dull.
Prior art United States patents of interest include the following: U.S. Pat. No. 4,390,338 to Bowers et al.; U.S. Pat. No. 4,225,303 to Crisci; U.S. Pat. No. 4,234,299 to Kuenzig et al.; and U.S. Pat. No. 4,497,623 to Beuscher.